Changed the "volumeOperatorSpec" type to a pointer

[Daimanta]

This change prevents empty structs being generated when the structs are serialized. This makes sure an unused field isn't added to every OGCAPI that does not use the Volume Operator.

Description

This change prevents empty structs being generated when the structs are serialized. This makes sure an unused field isn't added to every OGCAPI that does not use the Volume Operator. This is mostly a quality-of-life feature that tries to prevent confusion to the reader of a yaml struct.

Type of change

• Improvement of existing feature

Checklist:

• I've double-checked the code in this PR myself
• I've left the code better than before (boy scout rule)
• The code is readable, comments are added that explain hard or non-obvious parts.
• I've expanded/improved the (unit) tests, when applicable
• I've run (unit) tests that prove my solution works
• There's no sensitive information like credentials in my PR